Automatic self-cleaning strainers

ABSTRACT

An automatic self-cleaning strainer including a housing having a liquid inlet and outlet, a strainer drum having straining media in the periphery thereof, a backwash shoe arranged to normally engage the surface of the shoe exposed to the liquid inlet, and indexing means for intermittently effecting relative rotation between the shoe and drum in increments of arc about the axis of the drum and also effecting radial separation between the shoe and drum during incremental movement therebetween and reestablishing engagement of the shoe with the surface of the drum when such incremental movement has stopped.

United States Patent [451 Jan. 18, 1972 lCarr [54] AUTOMATICSELF-CLEANING STRAINERS [72] Inventor: Hugh B. Carr, McMurray, Pa.

[73] Assignee: S. Kinney Engineers, Inc., Carnegie, Pa.

[22] Filed: June 9, 1970 [2]] Appl. No.: 44,674

[52] US. CL ..2l0/333, 2 l0/4l3 [5i] Int. Cl. ..B0ld 25/38, BOld 29/24[58] FieldoiSearch ..2lO/333,4l3,4l4,4l5

[56] References Cited UNITED STATES PATENTS 2,066,479 1/1937 Maclsaac..2l0/4l5 X 3,074,560 1/1963 Kinney ..2l0/4ll X Primary ExaminerSamih N.Zaharna Attorney-Parmelee, Utzler & Welsh [57] ABSTRACT An automaticself-cleaning strainer including a housing having a liquid inlet andoutlet, a strainer drum having straining media in the periphery thereof,a backwash shoe arranged to normally engage the surface of the shoeexposed to the liquid inlet, and indexing means for intermittentlyeffecting relative rotation between the shoe and drum in increments ofare about the axis of the drum and also effecting radial separationbetween the shoe and drum during incremental movement therebetween andreestablishing engagement of the shoe with the surface of the drum whensuch incremental movement has stopped.

20 Claims, 10 Drawing Figures PATENIEU JAN 1 8 I972 SHEEI 2 [IF 3INVENTOR HUGH B. CARR II is Attorneys 1 AUTOMATIC SELF-CLEANINGSTRAINERS SPECIFICATION This invention relates to an automaticself-cleaning strainer, and particularly to such a strainer havingfeatures making it suitable for use in the fine straining (e.g., 250 tomicrons) of liquids. The commonly used automatic self-cleaning strainersincorporate a drum having straining media supported by it,through whichdirty liquid flows to be strained of solid matter. The straining mediais flushed of accumulated solid by liquid flowing in a reverse directionthrough the media and into a backwash shoe and out of the strainer. Thedrum and the shoe are rotated relative to each other so that successivesections of straining media are flushed. These type strainers areinherently limited, for all practical purposes, in size of solid matterwhich may be strained. For example, these strainerswould not be used toremove solid matter less than 0.010 inch in cross-sectional size. Whereit is desired to strain finer solids from the liquid, an additional finestrainer would have to be used.

In the case of a self-cleaning strainer having a rotating drum, theparticle size limitation is controlled by the minimum clearance whichcan be maintained between the drum and the fixed strainer housing. Thedirty incomingzliquid will tend to pass through the interface of thedrum and housing (i.e., short circuit) when the clearance there isgreater than the size of the straining media or when the media has somesolid accumulated thereon. Thus, liquid having fine particles will mixwith outlet liquid. The short-circuiting problem increases with age ofthe strainer. The rotating drum will wear the housing, the drum will getout of round, and the housing casting will grow, with all of theseresulting in an increase of the clearance between the drum and thehousing.

Another problem with the currently used automatic selfcleaning strainersis the reduction of backwash efficiency caused by the opening up ofclearances between the drum and backwash shoe. This problem is common torotating or stationary drum type strainers. Dirty liquid will passthrough the shoe-drum clearance to flood the shoe. This will reduce theamount of backwash liquid which can pass through the straining media.The backwash efiiciency will thereby be reduced. The clearance betweenthe backwash shoe and drum will get larger in time because of theconstant rubbing between the shoe and drum, and thus, the backwashefficiency will diminish accordingly.

I overcome the above-metioned problems by providing an automaticself-cleaning strainer in which tight clearances between the drum andhousing, and between the drum and backwash shoe are initially made andmaintained in time. Thus, a short circuiting is greatly reduced to allowfiner straining and improved backwashing efficiency. More particularly,I provide an automatic self-cleaning strainer which includes a backwashshoe normally engaging that surface of the drum which is exposed toinlet liquid, and indexing means for intermittently effecting relativerotation between the shoe and drum in increments of arc about the axisof the drum and also effecting radial separation between the shoe anddrums during the relative rotation therebetween and reestablishingengagement of the shoe with the surface of the drum when suchincremental relative rotation has stopped. By separating the shoe anddrum when they rotate relative to each other, tight initial clearancebetween the shoe and drum will be maintained because there will be norotational rubbing between the two elements. As a secondary feature,Lprovide means for always urging the shoe against the surface of thedrum, to thus insure continuing tight clearance between the shoe and thedrum. In the preferred form, the invention has a drum fixed to thestrainer housing and a backwash shoe normally engaging the insidesurface of the drum. The dirty liquid flows through the inside of thedrum. The fixed drum will permit initial installation with tightclearance between the drum and the strainer housing. In addition, sealscan be incorporated between the drum and strainer housing. Thus, shortcircuiting between the drum and strainer housing may be practicallyeliminated and thereby pennit the strainer to be used for finestraining. The backwash shoe disengages from the drum when the shoe ismoved relative to the drum and thereby results in continuing highbackwash efficiency.

Other details and advantages of the invention will become apparent asthe following descriptions of present preferred embodiments thereofproceed.

In the accompanying drawings I have shown present preferred embodimentsof the invention in which:

FIG. 1 is a view partly in vertical section and partly in elevation ofan automatic self-cleaning strainer constructed in accordance with thisinvention;

FIG. 2 is a view looking along the line II--Il of FIG. 1;

FIG. 3 is a view looking along the line III--III of FIG. 1;

FIG. 4 is a view looking along the line IVIV of FIG. 1;

FIG. 5 is a fragmentary section on a larger scale of the view shown inFIG. 4;

FIG. 6 is a fragmentary perspective view of the index wheel and guideroll forming part of this invention and shown in FIG.

FIG. 7 is a view looking along the line VII VII of FIG. 1 showing onesection of straining media as arranged in the drum element of thisinvention;

FIG. 8 is a view partly in vertical section and partly in elevation ofan automatic self-cleaning strainer constructed in accordance with thisinvention and showing another embodiment thereof;

FIG. 9 is a fragmentary section of the strainer of FIG. 8 showingrelationship of the elements of the backwash shoe assembly to thestrainer drum, and specifically showing the front shoe separated fromthe inner surface of the drum; and

FIG. 10 is a view looking along the line X-X of FIG. 8.

Referring now to the drawings, there is shown an automatic self-cleaningstrainer, generally designated by the numeral 20, including a generallycylindrical-shaped housing or body 22 having diametrically opposedliquid inlet 24 and outlet 26 openings. Arranged coaxially within body22 is a truncated cone-shaped strainer drum 28 with its narrow andfacing downwardly. The drum 28 is fixed between flange portions 30 and32 depending from the main portion of body 22. O-ring type seals 34 and36 of suitable rubber material, are arranged between the upper and lowercircumferential edge of drum 28 and flange portions 30 and 32,respectively. An annular keeper plate 38 bolted to the upper flange 30and the top of drum 28 serves to secure the drum within body 22. Drum 28is provided with a multiplicity of regularly spaced openingstherethrough for removably receiving straining media 40. The strainingmedia 40 preferably used with this invention, would be the kind capableof fine straining, that is, capable of straining solid matter having asize of anywhere from 250 microns to 10 microns. Straining media of wiremesh, perforated metal, nylon, or sintered metal, for example, wouldsatisfy the finestraining requirement. As shown in FIG. 7, the openingsthrough drum 28 are arranged in regular vertical sections so that thebackwash shoe opening, as will be more fully described hereinafter, willregister with or surround a complete section of openings without anyoverlap by the shoe of openings in the adjacent sections of drumopenings.

The interior of body 22 is provided with a structure which serves toguide dirty liquid from inlet 24 to the interior of drum 28 where theliquid will pass through the straining media 40 into cavity 42surrounding the drum 28 and then to outlet 26.

The straining media 40 are flushed clean by water flowing from cavity 42in a reverse direction into a backwash shoe 46 disposed on the interiorof drum 28. Backwash shoe 46 includes a hollow body having a large mouthportion 48 shaped to surround one section of openings through drum 28,as was mentioned previously. The mouth portion of backwash shoe 46 alsohas a tapered profile to conform with the interior surface of drum 28 sothat the mouth portion engages the interior surface of the drum. AnO-ring type seal ring 50 is arranged around the surface of the mouthportion 48 of backwash shoe 46 and serves to seal the interior of theshoe from the interior of the drum 28. The backwash shoe 46 is fixed toan intermediate portion of an elongated tube 52 arranged coaxially withdrum 28. Backwash shoe 46 has a discharge opening 54 communicating withthe interior of tube 52. Tube 52 has its lower end reciprocally-slidablyand rotatably arranged in the upper end portion of a backwash manifold56 bolted to the lower end portion of body 22. Backwash manifold 56 ishollow and includes a backwash liquid outlet 58 and a drain hole 59which is suitably plugged. Backwash outlet 58 may be connected withpiping 60, leading to a backwash liquid strainer open to atmosphere orwhatever, as desired. A shutoff valve 62 of any well-known constructionis placed in the piping 60 for opening and closing the backwash liquidflow. By virtue of the arrangement of tube 52, backwash manifold 56 andpiping 60, just described, backwash shoe 46 is open to atmosphere andthus pressurized liquid in cavity 42 will flow through the section ofstraining media 40 exposed to the backwash shoe, providing, of course,that valve 62 is open.

The upper end of tube 52 is fixed to a solid shaft 66 whichextendsupwardly through a central opening of a cover 68 removably fixed to thetop end portion of body 22. Shaft 66 is suitably reciprocally-slidablyand rotatably arranged within the central opening of cover 68, whichopening also houses a packing assembly 70 surrounding the shaft. Shaft66 extends upwardly into the confines of indexing assembly housing 74arranged on the top surface of cover 68. The housing 74 is secured tocover 68 by an adjusting ring 76 which may be loosened to permit thehousing 74 to be rotated relative to body 22 for aligning the mouthportion 48 of backwash shoe 46 with a section of straining media 40.Such an aligning is necessary to get proper indexing of backwash shoe 46with successive sections of media as the shoe is moved incrementallyaround drum 28. This indexing will be more fully appreciated as thisdescription progresses.

The upper end portion of shaft 66 is reciprocally slidably and rotatablysupported by a bearing member 78 arranged in a bearing housing 79depending from the main section of indexing housing 74. The upper end ofshaft 66 is fixed to the hub portion of index wheel 81 forming the camportion of the indexing means which is part of this invention and isgenerally designated by the reference numeral 80. The indexing wheel 81is fixed at its upper end to a spring housing 90. Ball bearings 91 aresupported in the upper section of spring housing 90, and a drive shaft92 is joumaled in the bearings. A helical coil spring 94 in compressionis arranged in spring housing 90 between bearings 91 and the hub ofindex wheel 81 to urge a downwardly directed force on the indexingwheel. This force is transmitted to shaft 66, to tube 52, and ultimatelyto backwash shoe The spring 94 thus serves as a pressure means forurging the backwash shoe 46 against the interior surface of drum 28.

The upper end of drive shaft 92 is coupled to a slotted plate member 96which is slidably arranged for reciprocal upward and downward movement.The slotted plate member 96 is operatively arranged with a drive roller97 which in turn is coupled to drive gears housed in gear unit 98coupled to electric motor 99 connected to a source of electrical power,not shown. The arrangement of the drive assembly comprising the platemember 96, drive roller 97, drive gear unit 98 and 99, just described,is a well-known arrangement for imparting reciprocal movement to thedrive shaft 92 which reciprocal movement is transmitted to the springhousing 90, index wheel 81, shaft 66, tube 52 and backwash shoe 46.

The indexing assembly 80 includes the index wheel 81 and guide assembly83 fixed to an intermediate portion of indexing assembly housing 74. Theindexing assembly 80 serves to guide the shaft 66, tube 52, and backwashshoe 46 in the reciprocal upward and downward movement, and alsorotatably in incremental arcs whereby the backwash shoe is positionedaround the interior of drum 28. lndex wheel 81 as shown in FIGS. 4-6, isformed with a series of longitudinally extending circumferentiallyspaced upper and lower bevelended teeth 81a and 81b, respectively. Upperand lower slots 81c and 81d, respectively, are defined between the upperand lower teeth. The lower teeth 81b are longitudinally aligned with theupper slots 81c, while the upper teeth 81a and lower slots 81d arelongitudinally aligned. The guide assembly 83 includes a guide roll 102rotatably mounted on a shaft 104 fixedly arranged in a cartridge 106received in an opening 108 through indexing assembly housing 74.Cartridge 106 is secured in place by cover 110 which is removably fixedto housing 74. Guide roll 102 is sized to be snugly received in slots81c and 814.

When it is desired to backwash the straining media 40, the valve 62 inpiping 60 is opened and liquid from cavity 42 flows freely in thereverse direction through the straining media into backwash shoe 46,then out of the backwash manifold 56. The backwashing sequence may betimed and controlled by coupling the backwash valve 62 with theoperation of motor 99 in any well-known manner. Thus, when the backwashshoe 46 is to be repositioned between successive sections of strainingmedia 40, the control will close valve 62 and start motor 99. Driveshaft 92 will first lift index wheel 81 and a slot 81c will moveupwardly of guide roll 102 until a lower tooth 81b engages the roll. Atthis point the backwash shoe 46 is disengaged or separated from theinterior surface of the drum 28. The separation of the backwash shoe 46from the drum 28 results because the shoe moves straight up and willthus separate sine it is shaped to the contour of the interior surfaceof the drum. When the beveled end of the lower tooth 81b engages theguide roll 102, a force is imparted to the guide wheel 81 to rotate itan incremental amount in the clockwise direction, or left as viewed inFIG. 6. A lower slot 81d will receive guide roll 102 at which point thedrive shaft 92 is driven reciprocally downwardly. Lower slot 81d isguided around guide roll 102 until the beveled end of an upper tooth 81aengages the roll and a force is imparted to the tooth to rotate theguide wheel 81 another incremental amount in the clockwise direction. Anupper slot 81c now receives guide roll 102 as the downward reciprocalmovement of the guide wheel 81 continues. A limit switch 106 will effectstoppage of the motor 99 when the lower limit of movement of the driveshaft 92 is reached. Thus, by virtue of the reciprocal-incrementalrotational movement just described, the backwash shoe 46 will moveupwardly out of engagement with the drum 28, rotate an incrementalamount in a clockwise direction, move slightly downwardly, rotateanother incremental amount in a clockwise direction and then movedownwardly to again engage the drum 28. The index assembly is sodesigned that the backwash shoe 46 is guided from section to section,successively, of straining media 40. The urging of spring 94 willprovide a tight reengagement of backwash shoe 46 with drum 28.

When the backwash valve 62 is closed during repositioning of thebackwash shoe 46, the hydraulic pressure in the backwash manifold 56would substantially equal the pressure in cavity 42. This pressure woulddevelop an upward thrust on the cross-sectional area of shaft 66, whichcould possibly prevent proper reengagement of the backwash shoe 46 withdrum 28. To avoid this possibility, the backwash valve 62 should beopened during the downstroke of the backwash shoe 46.

As mentioned earlier, the proper indexing of backwash shoe 46 betweensuccessive sections of straining media 40 is provided by making theindexing assembly housing 74 rotatably adjustable with respect to body22. Thus, the housing 74 would be rotated so that the opening of themouth portion 48 of backwash shoe 46 completely surrounds a section ofstraining media 40. Adjusting ring 76 would then be tightened to securehousing 74 to cover 68.

Since the drum 28 is fixed relative to the body 22, a very tight sealedfit is capable between the drum and the body. Because of this, an inlet24 may be effectively sealed from the cavity 42, thus avoiding shortcircuiting of dirty inlet liquid into the outlet cavity. As pointed outearlier, short circuiting would occur where the mesh size of thestrainer media was less than the clearance between the drum 28 and body22, and this short circuiting would, accordingly, limit the minimum sizeparticle which could be strained. By virtue of the tight fit between thedrum and body, this invention is particularly adaptable to linestraining. in addition, backwashing of the straining media is improvedby this invention because of the tight engagement between backwash shoe46 and drum 28, which engagement is maintained because surface wear ofthe shoe is minimized since it is disengaged from the drum duringrepositioning of the shoe on the drum. Backwash efficiency is alsoimproved by arranging the straining media 40 in sections, as described,enabling the backwash shoe to completely surround a section of mediawithout any overlap of adjacent sections by the shoe. This surroundingarrangement will avoid flooding of the backwash shoe 46, and thusimprove backwash efficiency.

Another embodiment of the present invention is illustrated in FIGS.0-10. The strainer of FIGS. 8-10 is generally designated by numeral 200and includes many of the same elements described and illustrated withregard to the first embodiments. Some of the same elements will not bedescribed again with the understanding that they form part of thissecond embodiment. Strainer 200 includes a drum 202 of generallycylindrical cross section provided with a multiplicity of regularopenings therethrough for removably receiving straining media 204. Theopenings through drum 202 are put in patterns similarto the uniformpattern of drum 28 so that when the backwash shoe assembly of thisembodiment is incrementally moved, a complete section of openings issurrounded by the backwash shoe. Drum 202 is fixed between flangeportions 30 and 32 depending from the main portion of body 22. O-ringseals 2% and 200 of suitable rubber material are arranged between theupper and lower circumferential edges of drum 202 and flange portions 30and 32, respectively.

A backwash shoe assembly, generally designated by the numeral 210, isfixed to an intermediate section of hollow tube 52, and includes a frontshoe 212 in engagement with the inner surface of drum 202 and a rearshoe 214 fixed at its radial inner end to the tube 52 and slidablysecured at its radial outer end with the radial inner end of front shoe212. The mating surfaces of the front shoe 212 and rear shoe 214 areinclined towards the tube 52. The front shoe 212 and rear shoe 214 aresecured to each other by means of plate 216 bolted to one side of rearshoe 214 and overlapping the inner edge portion of the front shoe, andplate 218 bolted to the other side of rear shoe 214 and overlapping theother inner edge of the front shoe.

Rings 220 and 222 are disposed in the inner portions of the upper andlower ends, respectively, of drum 202. Upper ring 220 is fixed to anannular plate 224 which in turn is fixed to the upper end surfaces ofdrum 202 and flange 30. The lower ring 222 is fixed in position as bywelding it to the drum 202. The rings 220 and 222 serve as upper andlower stops for the reciprocal movement of the front shoe 212. As thetube 52 is lifted in the manner described with regard to the firstembodiment, both the front shoe 212 and rear shoe 214 are liftedtogether. A slight clearance (viz, one-eighth inch) exists between thetop of the front shoe 212 and the lower surface of the upper ring 220,and as the front shoe 212 is lifted to contact ring 220 further upwardmovement of the front shoe is stopped. Rear shoe 2114 continues movingupwardly with the resultant action between the inclined mating surfacesof the front and rear shoes causing the front shoe 212 to separate fromengagement with the inner surface of drum 202. Rotation of both frontand rear shoes 212 and 214 will result, followed by downward translationof the rear shoe 214, then the additional incremental rotation of bothfront and rear shoe, and finally downward translation of both front andrear shoes where front shoe 212 is stopped by lower ring 222 at whichpoint rcar shoe 214 urges front shoe 212 against the inner surface ofthe drum 202.

The embodiment of strainer 200 of P108. 8-10 functions the same as theembodiment of FIGS. 1-7 and with the same results set forth with respectto the first embodiment. it is again noted that the only differencebetween the first and second embodiment is in the construction of thedrums and backwash shoe assemblies.

Many other modifications are contemplated within the scope of theessence of this invention. The drum could be made to rotateincrementally with the backwash shoe having been disengaged prior torotation, and then engaged when rotation is stopped. Although theincrementally rotating drum would not be as good as the stationary drumregarding sealing between the inlet and the outlet, it would beconsiderably better than a constantly rotating drum, as is commonlyused. The electrical motor 99 could be replaced by either a pneumatic orhydraulic motor. The timing between operation of the motors (i.e., theduration of backwash) may be simply controlled by a timing mechanism, aflow switch in the backwash outlet, a pressure drop controller arrangedbetween inlet 24 and outlet 26, or by any other well-known controllers.it should be apparent that even other modifications and embodiments arepossible within the scope of this invention as set forth in thefollowing claims.

I claim:

1. An automatic self-cleaning strainer comprising:

a housing having inlet and outlet means,

strainer drum means supported in said housing and having straining mediain the periphery thereof, said drum means being so arranged that liquidentering the inlet means flows through said media to the outlet means;

backwash shoe means arranged within said housing and normally engagedagainst that surface of said drum means which is exposed to the inletliquid and into which strained liquid backwashes through a selected areaof said drum means to flush solids therefrom;

indexing means for intermittently effecting relative rotation betweensaid shoe and drum means in increments of are about the axis of the drummeans and effecting radial separation between the shoe and drum meansduring the incremental relative rotation therebetween and reestablishingengagement of the shoe means with the surface of the drum means whensuch incremental relative rotation has stopped.

2. The automatic self-cleaning strainer as set forth in claim 1 whereinsaid straining media include individual strainer elements carried bysaid drum means; and said indexing means being indexed with respect tothe location of straining elements in the drum means and the dimensionsof said backwash shoe means being such that only the full areas of saidstrainer elements register with the shoe means any time the shoe meansis engaged with the drum means.

3. The automatic self-cleaning strainer as set forth in claim 1 whereinthe interior of said drum means communicates with said inlet means andthe exterior of said drum means communicates with said outlet means;said backwash shoe means is arranged to engage the interior surface ofsaid drum means.

4. The automatic self-cleaning strainer as set forth in claim 1 whereinsaid drum means is fixed to said housing; and said backwash shoe meansis rotatable with respect to said drum means.

5. The automatic self-cleaning strainer as set forth in claim 1 whereinsaid indexing means includes locking means for securing said backwashshoe means in engagement with said drum means between incrementalrelative rotation therebetween.

6. An automatic self-cleaning strainer, comprising:

a hollow housing having liquid inlet and outlet means;

strainer drum means supported in said housing and having straining mediasecure in openings extending therethrough, the interior of said drummeans communicating with said inlet means and the exterior of said drummeans communicating with said outlet means; backwash shoe means arrangedwithin said housing and normally seulably engaging an interior portionof said drum means and covering a section of straining media forreceiving backwash liquid flowing through such section of media from theexterior of said drum means and for discharging the backwash liquid fromsaid housing; and

indexing means supported by said housing and fixed to said shoe meansfor intermittently positioning said shoe means about the inner peripheryof said drum means and effecting separation of the shoe means from thedrum means during the repositioning thereof about said drum means andreestablishing engagement of the shoe means with the drum means whensuch repositioning is completed.

7. The automatic self-cleaning strainer as set forth in claim 6 whereinsaid indexing means is so constructed and arranged as to reciprocatesaid shoe means into and out of engagement with said drum means and torotate said shoe means between disengaged positions thereof with respectto said drum means.

8. The automatic self-cleaning strainer as set forth in claim 6including pressure means for urging said shoe means into engagement withsaid drum means.

9. The automatic self-cleaning strainer as set forth in claim 6 whereinsaid indexing means includes a cam and cam follower operatively engagingeach other for guiding said shoe means out of and into engagement withsaid drum means during repositioning of said shoe means about said drummeans.

10. The automatic self-cleaning strainer as set forth in claim 6 whereinsaid openings in said drum means are arranged in a pattern of successivelike sections; and wherein said shoe means is shaped such that an entireone of said sections is surrounded without any overlap of adjacentsections by said shoe means when same is in engagement with said drummeans.

11. The automatic self-cleaning strainer as set forth in claim 10including aligning means operative with said indexing means for aligningsaid shoe means with a section of said openings.

12. The automatic self-cleaning strainer as set forth in claim 10wherein said indexing means includes a cam and cam follower operativelyengaging each other for guiding said shoe means from engagement withsaid drum means and surrounding a section of openings to disengagementfrom said drum means and then into engagement with said drum means tosurround a next-successive section of openings.

13. An automatic self-cleaning strainer, comprising:

a hollow housing having liquid inlet and outlet means;

a truncated cone-shaped strainer drum means supported in said housingand having a plurality of straining media secured in circumferentiallyspaced openings extending therethrough, the interior of said drum meanscommunicating with said inlet means and the exterior of said drumcommunicating with said outlet means;

backwash shoe means arranged within said housing and sealably engagingan interior portion of said drum means and covering a section ofstraining media for receiving backwash liquid flowing through suchsection of media from the exterior of said drum means and fordischarging the backwash liquid from said housing; and

indexing means supported by said housing and fixed to said shoe meansfor selectively positioning said shoe means about the inner periphery ofsaid drum means, said indexing means including cam and cam followermeans operatively engaging each other for guiding said shoe meansreciprocally into and out of engagement with said drum means androtatably between disengaged positions of said shoe means.

14. The automatic self-cleaning strainer as set forth in claim 13including pressure means for urging said shoe means into engagement withsaid drum means.

15. The automatic self-cleaning strainer as set forth in claim 13wherein said openings in said drum means are arranged in a pattern ofsuccessive like sections; and wherein said shoe means is shaped suchthat an entire one of said sections is surrounded without any overlap ofadjacent sections by said shoe means when same is in engagement withsaid drum means.

16. The automatic self-cleaning strainer as set forth no claim 15wherein said cam and cam follower means are so constructed and arrangedsuch that said shoe means is guided from engagement with said drum meansreciprocally towards the wide end of the drum means and then rotatablyinto alignment with the next section of openings and then reciprocallyinto engagement with the drum means.

17. An automatic self-cleaning strainer, comprising:

a hollow housing having liquid inlet and outlet means;

a generally cylindrically shaped strainer drum means supported in saidhousing and having a plurality of straining media secured incircumferentially spaced openings extending therethrough, the interiorof said drum means communicating with said inlet means and the exteriorof said drum communicating with said outlet means;

backwash shoe means arranged within said housing and sealably engagingan interior portion of said drum means and covering a section ofstraining media for receiving backwash liquid flowing through suchsection of media from the exterior of said drum means and fordischarging the backwash liquid from said housing;

said backwash shoe means including a front shoe having an outer endportion normally engaging the interior surface of said drum means and aninner end inclined toward the axis of the drum means, a rear shoeslidably engaging and secured to said front shoe along the inner endthereof, and a hollow tube coaxial with said drum means supporting saidrear shoe and communicating with the interior of said rear shoe andfurther communicating with the exterior of said housing; first andsecond stop means supported at opposite ends,

respectively, of said drum means for limiting the axial movement of saidfront shoe with respect to said drum means;

indexing means supported by said housing and fixed to said backwash shoemeans for selectively positioning said shoe means about the innerperiphery of said drum means, said indexing means operatively engagingsaid tube to move same reciprocally with respect to said drum meanswhereby said front shoe is stopped by said first stop means and saidrear shoe continues to reciprocate to move said front shoe out ofengagement with said drum means and then rotatably into a nextsuccessive position where said tube is then moved reciprocally in theopposite direction where said front shoe is stopped by said second stopmeans and said rear shoe continues to reciprocate to move said frontshoe into engagement with said drum means.

18. The automatic self-cleaning strainer as set forth in claim 17including pressure means for urging said shoe means into and out ofengagement with said drum means.

19. The automatic self-cleaning strainer as set forth in claim 17wherein said openings in said drum means are arranged in a pattern ofsuccessive like sections; and wherein said front shoe is shaped suchthat an entire one of said sections is surrounded without any overlap ofadjacent sections by said front shoe when same is in engagement withsaid drum means.

20. The automatic self-cleaning strainer as set forth in claim 17wherein said first and second stop means include ring members fixed atopposite end portions of said drum means.

1. An automatic self-cleaning strainer comprising: a housing havinginlet and outlet means, strainer drum means supported in said housingand having straining media in the periphery thereof, said drum meansbeing so arranged that liquid entering the inlet means flows throughsaid media to the outlet means; backwash shoe means arranged within saidhousing and normally engaged against that surface of said drum meanswhich is expOsed to the inlet liquid and into which strained liquidbackwashes through a selected area of said drum means to flush solidstherefrom; indexing means for intermittently effecting relative rotationbetween said shoe and drum means in increments of arc about the axis ofthe drum means and effecting radial separation between the shoe and drummeans during the incremental relative rotation therebetween andreestablishing engagement of the shoe means with the surface of the drummeans when such incremental relative rotation has stopped.
 2. Theautomatic self-cleaning strainer as set forth in claim 1 wherein saidstraining media include individual strainer elements carried by saiddrum means; and said indexing means being indexed with respect to thelocation of straining elements in the drum means and the dimensions ofsaid backwash shoe means being such that only the full areas of saidstrainer elements register with the shoe means any time the shoe meansis engaged with the drum means.
 3. The automatic self-cleaning straineras set forth in claim 1 wherein the interior of said drum meanscommunicates with said inlet means and the exterior of said drum meanscommunicates with said outlet means; said backwash shoe means isarranged to engage the interior surface of said drum means.
 4. Theautomatic self-cleaning strainer as set forth in claim 1 wherein saiddrum means is fixed to said housing; and said backwash shoe means isrotatable with respect to said drum means.
 5. The automaticself-cleaning strainer as set forth in claim 1 wherein said indexingmeans includes locking means for securing said backwash shoe means inengagement with said drum means between incremental relative rotationtherebetween.
 6. An automatic self-cleaning strainer, comprising: ahollow housing having liquid inlet and outlet means; strainer drum meanssupported in said housing and having straining media secure in openingsextending therethrough, the interior of said drum means communicatingwith said inlet means and the exterior of said drum means communicatingwith said outlet means; backwash shoe means arranged within said housingand normally sealably engaging an interior portion of said drum meansand covering a section of straining media for receiving backwash liquidflowing through such section of media from the exterior of said drummeans and for discharging the backwash liquid from said housing; andindexing means supported by said housing and fixed to said shoe meansfor intermittently positioning said shoe means about the inner peripheryof said drum means and effecting separation of the shoe means from thedrum means during the repositioning thereof about said drum means andreestablishing engagement of the shoe means with the drum means whensuch repositioning is completed.
 7. The automatic self-cleaning straineras set forth in claim 6 wherein said indexing means is so constructedand arranged as to reciprocate said shoe means into and out ofengagement with said drum means and to rotate said shoe means betweendisengaged positions thereof with respect to said drum means.
 8. Theautomatic self-cleaning strainer as set forth in claim 6 includingpressure means for urging said shoe means into engagement with said drummeans.
 9. The automatic self-cleaning strainer as set forth in claim 6wherein said indexing means includes a cam and cam follower operativelyengaging each other for guiding said shoe means out of and intoengagement with said drum means during repositioning of said shoe meansabout said drum means.
 10. The automatic self-cleaning strainer as setforth in claim 6 wherein said openings in said drum means are arrangedin a pattern of successive like sections; and wherein said shoe means isshaped such that an entire one of said sections is surrounded withoutany overlap of adjacent sections by said shoe means when same is inengagement with said drum means.
 11. The automatic self-cleaningstrainer as set forth in claim 10 incLuding aligning means operativewith said indexing means for aligning said shoe means with a section ofsaid openings.
 12. The automatic self-cleaning strainer as set forth inclaim 10 wherein said indexing means includes a cam and cam followeroperatively engaging each other for guiding said shoe means fromengagement with said drum means and surrounding a section of openings todisengagement from said drum means and then into engagement with saiddrum means to surround a next-successive section of openings.
 13. Anautomatic self-cleaning strainer, comprising: a hollow housing havingliquid inlet and outlet means; a truncated cone-shaped strainer drummeans supported in said housing and having a plurality of strainingmedia secured in circumferentially spaced openings extendingtherethrough, the interior of said drum means communicating with saidinlet means and the exterior of said drum communicating with said outletmeans; backwash shoe means arranged within said housing and sealablyengaging an interior portion of said drum means and covering a sectionof straining media for receiving backwash liquid flowing through suchsection of media from the exterior of said drum means and fordischarging the backwash liquid from said housing; and indexing meanssupported by said housing and fixed to said shoe means for selectivelypositioning said shoe means about the inner periphery of said drummeans, said indexing means including cam and cam follower meansoperatively engaging each other for guiding said shoe means reciprocallyinto and out of engagement with said drum means and rotatably betweendisengaged positions of said shoe means.
 14. The automatic self-cleaningstrainer as set forth in claim 13 including pressure means for urgingsaid shoe means into engagement with said drum means.
 15. The automaticself-cleaning strainer as set forth in claim 13 wherein said openings insaid drum means are arranged in a pattern of successive like sections;and wherein said shoe means is shaped such that an entire one of saidsections is surrounded without any overlap of adjacent sections by saidshoe means when same is in engagement with said drum means.
 16. Theautomatic self-cleaning strainer as set forth in claim 15 wherein saidcam and cam follower means are so constructed and arranged such thatsaid shoe means is guided from engagement with said drum meansreciprocally towards the wide end of the drum means and then rotatablyinto alignment with the next section of openings and then reciprocallyinto engagement with the drum means.
 17. An automatic self-cleaningstrainer, comprising: a hollow housing having liquid inlet and outletmeans; a generally cylindrically shaped strainer drum means supported insaid housing and having a plurality of straining media secured incircumferentially spaced openings extending therethrough, the interiorof said drum means communicating with said inlet means and the exteriorof said drum communicating with said outlet means; backwash shoe meansarranged within said housing and sealably engaging an interior portionof said drum means and covering a section of straining media forreceiving backwash liquid flowing through such section of media from theexterior of said drum means and for discharging the backwash liquid fromsaid housing; said backwash shoe means including a front shoe having anouter end portion normally engaging the interior surface of said drummeans and an inner end inclined toward the axis of the drum means, arear shoe slidably engaging and secured to said front shoe along theinner end thereof, and a hollow tube coaxial with said drum meanssupporting said rear shoe and communicating with the interior of saidrear shoe and further communicating with the exterior of said housing;first and second stop means supported at opposite ends, respectively, ofsaid drum means for limiting the axial movement of said front shoe withrespect to said drum means; indexing means suppoRted by said housing andfixed to said backwash shoe means for selectively positioning said shoemeans about the inner periphery of said drum means, said indexing meansoperatively engaging said tube to move same reciprocally with respect tosaid drum means whereby said front shoe is stopped by said first stopmeans and said rear shoe continues to reciprocate to move said frontshoe out of engagement with said drum means and then rotatably into anext successive position where said tube is then moved reciprocally inthe opposite direction where said front shoe is stopped by said secondstop means and said rear shoe continues to reciprocate to move saidfront shoe into engagement with said drum means.
 18. The automaticself-cleaning strainer as set forth in claim 17 including pressure meansfor urging said shoe means into and out of engagement with said drummeans.
 19. The automatic self-cleaning strainer as set forth in claim 17wherein said openings in said drum means are arranged in a pattern ofsuccessive like sections; and wherein said front shoe is shaped suchthat an entire one of said sections is surrounded without any overlap ofadjacent sections by said front shoe when same is in engagement withsaid drum means.
 20. The automatic self-cleaning strainer as set forthin claim 17 wherein said first and second stop means include ringmembers fixed at opposite end portions of said drum means.